The present invention relates to optical microelectromechanical system (MEMS) and, more particularly, to apparatus and method for sensing switching positions of a MEMS optical switch.
Modem technology has enabled MEMS devices to be fabricated on semiconductor substrates, typically silicon substrates. These MEMS devices typically have sizes in the order of microns and may be integrated with other electrical circuits on a common substrate. As a result, MEMS devices have found their way into numerous applications across numerous industries. Exemplary MEMS applications include optical switching, optical attenuators, inertial or pressure sensors, and biomedical devices.
Generally, a MEMS optical switch has a mirror that can be extended and retracted in various positions. In one instance, the mirror can be extended to interpose between optical channels such that optical beams traveled in the channels are reflected. In another instance, the mirror can be retracted to be away from the optical channels such that optical beams traveled in the channels pass through without being reflected. Accordingly, depending on the position of the mirror, the optical beams can be switched into different optical channels. Yet in a MEMS optical attenuator instance, the mirror can be extended in a position that a part of optical beams traveled in the channels are reflected, and a part of the optical beams traveled in the channels pass through without being reflected. Accordingly, depending on the position of the mirror, different attenuation of the optical beams can be arranged.
An exemplary MEMS optical switch is described in a co-pending U.S. patent application Ser. No. 09/372,265, filed Aug. 11, 1999, entitled xe2x80x9cMICROELECTROMECHANICAL OPTICAL SWITCH AND METHOD OF MANUFACTURE THEREOFxe2x80x9d, now U.S. Pat. No. 6,229,640 commonly assigned to ADC Telecommunications, Inc., which is incorporated herewith by reference. Another exemplary MEMS optical switch is described in a co-pending U.S. patent application Ser. No. 09/768,723, filed Jan. 24, 2001, entitled xe2x80x9cMEMS OPTICAL SWITCH ON A SINGLE CHIP AND METHODxe2x80x9d, commonly assigned to ADC Telecommunications, Inc., which is incorporated herewith by reference.
In a typical MEMS device, a mirror is supported by a suspension structure, and an actuator drives the mirror into different positions depending on the polarity and amount of power applied to the actuator. Typically, when no power is applied to the actuator, the mirror is moved back to the original position by the force of the bent suspension structure caused by the power.
Position sensing in a MEMS optical switch becomes very important to monitor the switch""s performance and to provide feedback in case of failure for switching controlling.
Therefore, improvements on monitoring switch""s performance and control of MEMS optical switches are desired.
In accordance with this invention, the above and other problems were solved by providing a position sensing apparatus for sensing switching positions in a MEMS device.
In one embodiment of the present invention, the position sensing apparatus is provided in a MEMS device that includes a suspension structure, an actuator, and a support structure. The position sensing apparatus includes a first contact that is disposed on the suspension structure, a second contact that is coupled to the support structure, and an indicator that is coupled to one of the first and second contacts. When the first and second contacts are in contact with each other, the indicator provides a first signal. When the first and second contacts are not in contact, the indicator provides a second signal.
Still in one embodiment of the present invention, the first contact is disposed on the suspension structure that is moveable when power is applied to the actuator, and the second contact is disposed on a deflection beam. A first end of the deflection beam is mounted on the support structure, and a second end of the deflection beam is deflectable when the first contact contacts the second contact.
In another embodiment of the present invention, the suspension structure includes a spring, the first contact is disposed on the spring that is moveable when power is applied to the actuator, and the second contact is a stationary contact.
Further in one embodiment of the present invention, the first contact is electrically connected to a ground voltage or potential, and the second contact is electrically connected to a pre-set voltage. The indicator includes a resistor and a buffer. The second contact is electrically connected to a node between the resistor and the buffer. The other end of the resistor is connected to a voltage supply, and the other end of the buffer is an output of the indicator. The output of the indicator provides the first signal and the second signal.
Accordingly, when power is applied to the actuator, a mirror that is mounted on the suspension structure is switched to a first position, and meanwhile the first and second contacts are in contact with each other such that the indicator provides the first signal that indicates that the mirror is switched to the first position. When no power is applied to the actuator, the mirror is switched to a second position, and meanwhile the first and second contacts are not in contact such that the indicator provides the second signal that indicates that the mirror is switched to the second position. An operator can easily monitor the switching positions of the mirror within a MEMS device.
Yet in one embodiment of the present invention, the indicator includes a resistor and an exclusive-or logic gate. The second contact is electrically connected to a node between the resistor and a first input of the exclusive-or logic gate. The other end of the resistor is connected to a voltage supply, and a second input of the exclusive-or logic gate is connected to a node between a resistor divider. The resistor divider has a first resistor connected to the power applied to the actuator, and a second resistor connected to the ground voltage or potential. An output of the exclusive-or logic gate is an output of the indicator that provides the first signal and the second signal. Accordingly, an operator can easily monitor the switch""s performance of a MEMS device and provide feedback in case of switching failure or errors of the MEMS device.
Additionally in one embodiment of the present invention, the contacts of the position sensing apparatus can be fabricated with the rest of a MEMS chip structure, and the indicator can be built in with an actuator driven circuit.
One of the advantages of the present invention is that it provides a simple, durable, and cost effective mechanism for monitoring the switch""s performance of a MEMS device.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.